This long-term program of research into electrophysiological correlates of psychiatric illness aims to provide objective aids to psychiatric diagnosis and also clues to the dysfunctional neurophysiological mechanisms underlying these disorders. EEG and evoked potentials (EPs) are recorded in different, clinical groups and analyzed by computer. The rheoencephalogram (REG) is recorded; it is a noninvasive method for measuring regional cerebral blood flow by impedance plethysmography. Subjects are assessed clinically by standardized interviews, rating scales and personality inventories to provide systematic diagnostic, symptom pattern, and personality classification criteria that can be related to electrophysiological measures. Patients are retested in various stages of treatment. EPs are recorded from 16 locations in two paradigms: a) under passive conditions, with intermingled stimuli of several sensory modalities (electrocutaneous over left and right median nerves, visual pattern, auditory click); b) selective attention, subject required to count one of four randomly intermingled stimuli. Brainstem potentials are also recorded in the paradigm (a) session. Specific aims include: a) Replication and extension of previously found EP and EEG correlates of psychopathology, e.g., differences between schizophrenics and neurotics and between neurotics and normals. b) Determination of psychoactive drug effects on EP and EEG measures. c) Development and validation of an electrodiagnostic system based on EP and EEG measures that give replicable discriminations and are relatively insensitive to drugs. d) Determination of REG correlates of psychopathology, including discrimination between dementia and depression. e) By comparing attention-related changes in sequential EP events, to define the stages at which sensory information processing may be defective in various psychiatric disorders; a specific hypothesis to be tested is that defects in sensory "filtering" occur earlier in schizophrenia than in major depression. Disciplines involved include psychiatry, electrophysiology, clinical psychology and psychobiology.